Boards such as module boards, on which IC chips and chip components are mounted, have been conventionally connected to each other by a substrate joining member. The substrate joining member includes a multi-pole connector formed of a plug and a socket, or a pin connector formed of multiple connecting pins fixed to a spacer made of resin.
Meanwhile mobile devices have been downsized, light-weighted and yet sophisticated, which increases the number of connecting terminals between module boards while a pitch between each one of the connecting terminals becomes narrower. The substrate joining member thus needs to be downsized so that an area per pin can be desirably smaller.
However, the foregoing connecting structure tends to subject a connected section of the pin connector to great force when a change in temperature causes the members forming this connected section to change differently in dimensions or when this connected section receives external impact. Thus a structure for easing such external force has been studied.
For instance, use of pin connector 130 shown in FIGS. 10A and 10B for connecting module boards 110 and 120 together as shown in FIG. 11 allows easing stress produced by thermal expansion of resin spacer 132. This is disclosed in patent document 1. FIG. 10A shows a plan view of conventional pin connector 130, and FIG. 10B shows a sectional view cut along a longitudinal direction of pin connector 130. FIG. 11 shows a sectional view illustrating module boards 110 and 120 coupled together with pin connector 130. Resin spacer 132 of this pin connector 130 includes multiple metal connecting pins 134 vertically extending through spacer 132. Pins 134 are insert-molded together with resin spacer 132, thereby being fixed to spacer 132. On top of that, as shown in FIG. 10B, pin connector 130 is provided with resilient legs 136 slantingly protruding from its underside at both ends.
As shown in FIG. 11, module boards 110 and 120 are connected with this pin connector 130. To be more specific, metal connecting pin 134 extends through circuit patterns 114 and 124 at its upper end and lower end, then the upper end of pin 134 is soldered with circuit pattern 124, and the lower end of pin 134 is soldered with circuit pattern 114, thereby forming soldered sections 128. At this time, module board 110 at lower side is brought into contact with and fixed to resilient legs 136 provided to the underside of spacer 132.
If resin spacer 132 of pin connector 130 thermally expands due to the heat generated by electronic components 116, 126 or a change in ambient temperature, the stress due to these heat and changes can be absorbed by resilient legs 136. As a result, soldered section 128 incurs no stress even if components generate heat, so that a stable soldered condition can be maintained. Resilient legs 136 can be provided also to the top face of spacer 132 in addition to the underside thereof.
Connection between a hybrid integrated circuit and a base circuit board employs a rectangular parallelepiped and heat resistant resin into which perimeter a number of U-shaped conductors are inserted at given intervals, so that the hybrid integrated circuit is electrically and mechanically coupled to the base circuit board. A lead-array terminal formed of these U-shaped conductors contacts with a land electrode of the base circuit board, and at this contacting place, a soldered section and a non-soldered section are defined by a step. When force is applied vertically to the base circuit board, the foregoing structure allows the non-soldered section to be bent with ease at the step, so that the force can be absorbed, thereby preventing the soldered section from receiving excessive stress (e.g. refer to patent document 2).
When another circuit board is fixed to the base circuit board with an external connecting lead wire, a tip of this lead wire is bent to be resilient. This is an improvement. This resilient section can absorb the distortion due to a difference in thermal expansion coefficients between this another circuit board and the base circuit board, so that both of the circuit boards can be coupled together in a good condition (e.g. refer to patent document 3).
The mobile devices have been sophisticated conspicuously in recent years, so that the number of connecting terminals of connectors has continued to increase while the mobile devices are required to be tougher against drop impact. The connecting structure by using pin connectors discussed above provides through holes to a module board, and the connecting pins extend through these holes, so that the module board is connected to a circuit pattern. On top of that, the resilient legs absorb thermal stress. This structure, however; uses both sides of the module board inefficiently, and the presence of through holes constrains the board from increasing a density of the circuit pattern.
The market expects that a circuit pattern be of a higher density and a lead shape be smaller, so that simple tricks such as a modification of a connecting lead-wire terminal are not enough to dampen the stress.    Patent Document 1: Unexamined Japanese Patent Publication No. H06-310195    Patent Document 2: Japanese Utility Model Publication No. H05-55575    Patent Document 3: Japanese Utility Model Publication No. H01-86268